What causes "found a token with no parent" in biomejs/biome?

Update to the latest Biome release

found a token with no parent

Error message

found a token with no parent

What it means

Panic in the Grit format-on-type handler (grit.rs:477). The handler calls token.parent() on the token found at the cursor; in rowan trees the root is a node, so tokens from token_at_offset always have a parent. This is a defensive assertion for a state (detached or token-rooted tree) the parser cannot produce.

Source

Thrown at crates/biome_service/src/file_handlers/grit.rs:477

        // File is empty, do nothing
        TokenAtOffset::None => panic!("empty file"),
        TokenAtOffset::Single(token) => token,
        // The cursor should be right after the closing character that was just typed,
        // select the previous token as the correct one
        TokenAtOffset::Between(token, _) => token,
    };

    if token.text_trimmed_range().end() != offset {
        return Ok(format_on_type_noop(offset));
    }

    if !matches_on_type_char(token.text_trimmed()) {
        return Ok(format_on_type_noop(offset));
    }

    let root_node = match token.parent() {
        Some(node) => node,
        None => panic!("found a token with no parent"),
    };

    if root_node
        .ancestors()
        .any(|node: GritSyntaxNode| node.kind().is_bogus())
    {
        return Ok(format_on_type_noop(offset));
    }

    let formatting_root = root_node
        .ancestors()
        .find(|node: &GritSyntaxNode| {
            node.parent()
                .is_some_and(|parent| parent.kind() == GritSyntaxKind::GRIT_ROOT)
        })
        .unwrap_or(root_node);

    let printed =

View on GitHub (pinned to 405dedb0ff)

Solutions

Update to the latest Biome release
Report a reproducer (document + keystroke) to https://github.com/biomejs/biome/issues if found
Embedders: guard on-type formatting with catch_unwind and treat failure as no-op

Defensive patterns

Strategy: fallback

Try / catch

// LSP client - best-effort on-type formatting
try {
  const edits = await client.sendRequest('textDocument/onTypeFormatted', params);
} catch {
  // ignore: formatting is optional, typing must never block
}

Prevention

Wrap all optional formatting requests in best-effort error handling
Pin a known-good Biome version
Report reproductions upstream; this arm should be unreachable in practice

When it happens

Trigger: Not reachable via normal LSP requests; only a detached token or token-rooted tree would trigger it.

Common situations: Essentially theoretical; surfacing only with hand-constructed trees or internal API misuse.

Related errors

AI-assisted analysis of biomejs/biome@405dedb0ff (2026-08-20). Data as JSON: /api/errors/e175d80d29108244. Report an issue: GitHub.